PMR-15 polyimide is a high performance polymer that is widely used in high temperature applications of composites. The presence of free radicals at room temperature in this polyimide has been confirmed recently by electron paramagnetic resonance (EPR, or ESR) spectroscopy of PMR-15 resin samples. These free radicals are generated when the resin samples are exposed to temperatures above 300oC and are found to be relatively stable at room temperatures. The weight loss data at an elevated temperature suggest that the free radicals are directly involved in the oxidative degradation of the polyimide in the presence of oxygen. The goal of this project is to measure the static magnetic susceptibility of a PMR-15 resin sample using a superconducting quantum interference device (SQUID) magnetometer and compared the susceptibility data with EPR results reported earlier. This year, we have characterized the aging process of a few polyimide composites with W-band EPR. In addition we have carried out a pilot EPR study of teflon-based shielding that NASA brought back from the Hubbell telescope in orbit.